Backpack



FIG. 1 is a top, front, left perspective view of a backpack showing my new design;

FIG. 2 is a front view thereof;

FIG. 3 is a rear view thereof;

FIG. 4 is a right side view thereof;

FIG. 5 is a left side view thereof;

FIG. 6 is a top view thereof; and,

FIG. 7 is a bottom view thereof.

The broken lines within the shaded areas depict stitching that forms no part of the claimed design. The broken lines within the unshaded area of FIG. 7 show features that form no part of the claimed design. 

CLAIM The ornamental design for a backpack, as shown and described. 